This invention relates to a small, lightweight, highly efficient portable device for regulating the luminous flux output of a battery powered headlamp. Wildland firefighters use a hard-hat mounted headlamp to provide illumination for night fire suppression activities. It is desirable to have the headlamp and battery both located on the hard-hat to eliminate the need for an interconnecting cord which could entangle in brush. The headlamp and battery must be lightweight so as to not burden the firefighter and the battery must contain sufficient energy to power the headlamp for a complete night shift. Also, the light output must remain sufficient to provide adequate illumination for safe working conditions.
Current headlamps are powered by four "D" size carbon-zinc cells which are carried on the belt and are connected to the hard-hat mounted headlamp by a cord. These cells are too heavy to be carried on the hard-hat. Batteries suitable for carrying on the hard-hat are the "D" size lithium-sulfur dioxide and the zinc-air pack. Both provide adequate capacity, are lightweight and have flat discharge characteristics to provide nearly constant illumination through their useful life. However, the lithium-sulfur dioxide cell cannot be transported on passenger carrying aircraft and Zinc-Air packs have not been manufactured in sufficient quantity to meet the demand.
Six "AA" size alkaline-manganese dioxide cells have adequate energy content. However, without regulation their steep discharge voltage curve causes the illumination from the headlamp to drop off at an unacceptable rate. Therefore, a switching power regulator is used to provide nearly constant luminous flux output.
Devices for regulating the output flux of a lamp are well known. For example, U.S. Pat. No. 4,156,166 issued May 22, 1979, discloses and claims an apparatus for regulating the output flux of a lamp powered by a degenerating source of power, the output of said lamp being maintained substantially constant over a range of voltages by switching the power supply to the lamp on and off on a controlled duty cycle. By use of this method safety devices give an output of constant light until a lower voltage level is reached by the regulated power supply compared with an unregulated power supply. However, while the devices described in the above Shapiro et. al. patent allow greater utilization of the power supply than use without regulation, a major drawback is the electrical efficiency of the system as defined by the ratio of the power out to the power in of the system. Shapiro et. al. circuits would net near zero energy savings since power to run the circuits would probably be near the increase in usable battery power resulting from use of the circuits. Thus, net energy savings would be minimal.
U.S. Pat. No. 4,238,709 to Wallace which issued on Dec. 9, 1980 describes a device for manual control of one output intensity of a battery powered lamp. As battery output decreases the lamp output must be manually adjusted to keep its output constant. The circuit is designed for a hard-hat mounted lamp with power derived from a belt worn power pack. The lamp on/off time is controlled by the duty cycle of an astable oscillator which is controlled by the manual setting of a potentimeter.
A requisite for increasing the electrical efficiency of a regulating device is to limit the number of power consuming elements in the regulating device as well as using components of minimum energy requirements. For instance the invention as outlined in FIG. 3b, the preferred embodiment of this invention has only six components and an electrical efficiency of 88%.
Accordingly, the objectives of the present invention are to provide a highly energy efficient, light weight, compact, simple power switching device for battery powered helmet mounted headlamps, flashlights, or the like. The operation of the device provides a net increase in the useful utilization of the battery energy as compared to heretofore used devices and thereby increased battery life.